Many electric and hybrid electric vehicles employ both a conventional antiskid braking system and a regenerative braking system. The antiskid braking system typically includes several frictional drum or disc type braking assemblies which are selectively actuated by a hydraulic system. A control system modulates the hydraulic pressure applied to the frictional braking assemblies in a manner which controls the slippage of the vehicle's wheels relative to the road surface. The regenerative braking system within these vehicles utilizes the vehicle's electric motor to provide a negative torque to the driven wheels and converts the vehicle's kinetic energy to electrical energy for recharging the vehicle battery or power supply.
In one type of braking system, commonly referred to as a parallel braking system, the vehicle utilizes both traditional (i.e., friction braking) and regenerative braking during most instances. However, upon detection of an antiskid braking event, the system rapidly reduces the regenerative braking force and increases the amount of force provided by the antiskid braking system. This reduction or elimination of the regenerative braking force during antiskid events is required due to the inability and/or difficulty of the regenerative braking system to accurately provide a modulated braking force at the same frequency as the antiskid braking system, and due the tendency of the regenerative braking system to “work against” or impair the operation of the antiskid braking system during these events.
One drawback with these prior systems is that they frequently eliminate or “shut down” the regenerative braking system upon sensing any potential antiskid event.
During some antiskid events, the regenerative braking system will operate properly and will not impair the function of the antiskid braking system. Particularly, the regenerative braking system will not effect the operation of the antiskid braking system during events that are detected and/or occur only at the non-driven wheels (e.g., the wheels of the vehicle which are not driven by the electric motor). Thus, by disabling the regenerative braking function during these events, these prior systems unnecessarily lose the power-generating capabilities of the regenerative braking system during these events. Furthermore, these systems also suffer from an inconsistent braking “feel”, due to the temporary power loss incurred when the regenerative torque is eliminated.
There is therefore a need for a system and a method for regenerative and antiskid braking within an electric or hybrid electric vehicle that provides improved performance, efficiency and reliability.